Re: Kent & North Wales Light Railway: New Boy
There is a guy in Germany called Manfred Grünig, who sells the stuff, but more importantly runs training courses to teach how to do it. Next one, according to his website is 17/18 May. Essentially, the technique is well-known, and uses copper electric cable, twisted in to ever thinner branches, with a mix of plaster and paint to cover. P.S. Trees are generally grey, not brown

The choice of foliage is up to you. He sells stuff or you can use the usual suspects such as Woodland Scenics, etc. But I think that the trick that he has is that he studies very carefully what trees actually look like. So while twisting copper wire is the one thing, the other is to practice getting the 3D shape right. And I haven´t found anyone who is better at it, yet.